Orrery in the context of "Planetarium"

The Antikythera mechanism (/ˌæntɪkɪˈθɪərə/ AN-tik-ih-THEER-ə, US also /ˌæntaɪkɪˈ-/ AN-ty-kih-) is an ancient Greek hand-powered orrery (model of the Solar System). It is the oldest known example of an analogue computer. It could be used to predict astronomical positions and eclipses decades in advance. It could also be used to track the four-year cycle of athletic games similar to an olympiad, the cycle of the ancient Olympic Games.

The artefact was among wreckage retrieved from a shipwreck off the coast of the Greek island Antikythera in 1901. In 1902, during a visit to the National Archaeological Museum in Athens, it was noticed by Greek politician Spyridon Stais as containing a gear, prompting the first study of the fragment by his cousin, Valerios Stais, the museum director. The device, housed in the remains of a wooden-framed case of (uncertain) overall size 34 cm × 18 cm × 9 cm (13.4 in × 7.1 in × 3.5 in), was found as one lump, later separated into three main fragments which are now divided into 82 separate fragments after conservation efforts. Four of these fragments contain gears, while inscriptions are found on many others. The largest gear is about 13 cm (5 in) in diameter and originally had 223 teeth. All these fragments of the mechanism are kept at the National Archaeological Museum, along with reconstructions and replicas, to demonstrate how it may have looked and worked.

A Philosopher Lecturing on the Orrery, or the full title, A Philosopher giving that Lecture on the Orrery in which a lamp is put in place of the Sun, is a 1766 painting by Joseph Wright of Derby depicting a lecturer giving a demonstration of an orrery – a mechanical model of the Solar System – to a small audience. It is now in the Derby Museum and Art Gallery The painting preceded his similar An Experiment on a Bird in the Air Pump (National Gallery, London).

The first of Wright's candlelit masterpieces, Three Persons Viewing the Gladiator by Candlelight, was painted in 1765, and showed three men studying a small copy of the "Borghese Gladiator". The Gladiator was greatly admired; but his next painting, The Orrery, caused a greater stir, as it replaced the Classical subject at the centre of the scene with one of a scientific nature. Wright's depiction of the awe produced by scientific "miracles" marked a break with previous traditions in which the artistic depiction of such wonder was reserved for religious events, since to Wright the marvels of the technological age were as awe-inspiring as the subjects of the great religious paintings.

Solar System models, especially mechanical models, called orreries, that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale. The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the Solar System a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12,000 times the diameter of the Earth.

If the smaller planets are to be easily visible to the naked eye, large outdoor spaces are generally necessary, as is some means for highlighting objects that might otherwise not be noticed from a distance. The Boston Museum of Science had placed bronze models of the planets in major public buildings, all on similar stands with interpretive labels. For example, the model of Jupiter was located in the cavernous South Station waiting area. The properly-scaled, basket-ball-sized model is 1.3 miles (2.14 km) from the model Sun which is located at the museum, graphically illustrating the immense empty space in the Solar System.